Section 1 General Rules

Grounding and protective measures for electrical safety. Application area. Terms and Definitions

Encyclopedia of radio electronics and electrical engineering / Rules for the installation of electrical installations (PUE)

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1.7.1. This chapter of the Rules applies to all electrical installations of alternating and direct current with a voltage of up to 1 kV and above and contains general requirements for their grounding and protection of people and animals from electric shock both in normal operation of the electrical installation and in case of damage to the insulation.

Additional requirements are given in the relevant chapters of the EMP.

1.7.2. Electrical installations in relation to electrical safety measures are divided into:

• electrical installations with voltages above 1 kV in networks with solidly grounded or effectively grounded neutral (see 1.2.16);
• electrical installations with voltages above 1 kV in networks with isolated or grounded neutral through an arcing reactor or resistor;
• electrical installations with voltage up to 1 kV in networks with dead-earthed neutral;
• electrical installations with voltage up to 1 kV in networks with isolated neutral.

1.7.3. For electrical installations with voltage up to 1 kV, the following designations are accepted:

• TN system - a system in which the neutral of the power source is solidly grounded, and the open conductive parts of the electrical installation are connected to the solidly grounded neutral of the source by means of zero protective conductors;
• TN-C system - a TN system in which the zero protective and zero working conductors are combined in one conductor throughout its entire length (Fig. 1.7.1);
• TN-S system - TN system in which the zero protective and zero working conductors are separated along its entire length (Fig. 1.7.2);
• TN-CS system - a TN system in which the functions of the zero protective and zero working conductors are combined in one conductor in some part of it, starting from the power source (Fig. 1.7.3);
• IT system - a system in which the neutral of the power source is isolated from the ground or grounded through devices or devices with high resistance, and the open conductive parts of the electrical installation are grounded (Fig. 1.7.4);
• TT system - a system in which the neutral of the power source is solidly grounded, and the open conductive parts of the electrical installation are grounded using a grounding device that is electrically independent of the solidly grounded neutral of the source (Fig. 1.7.5).

The first letter is the state of the neutral of the power supply relative to earth:

• T - grounded neutral;
• I - isolated neutral.

The second letter is the state of open conductive parts relative to ground:

• T - open conductive parts are grounded, regardless of the relation to the earth of the neutral of the power source or any point of the supply network;
• N - open conductive parts are connected to a dead-earthed neutral of the power source.

Subsequent (after N) letters - combination in one conductor or separation of the functions of the zero working and zero protective conductors:

• S - zero working (N) and zero protective (PE) conductors are separated;
• C - the functions of the zero protective and zero working conductors are combined in one conductor (PEN-conductor);
• N - - zero working (neutral) conductor;
• RE - - protective conductor (grounding conductor, zero protective conductor, protective conductor of the potential equalization system);
• PEN- - combined zero protective and zero working conductors.

(click to enlarge)

Zero protective and zero working conductors are combined in one conductor:

• 1 - grounding conductor of the neutral (middle point) of the power source;
• 2 - open conductive parts;
• 3 - DC power supply

Rice. 1.7.1. TN-C system of alternating (a) and direct (b) current.

(click to enlarge)

Zero protective and zero working conductors are separated:

• 1 - grounding conductor of the neutral of the alternating current source;
• 1-1 - ground electrode of the output of the DC source;
• 1-2 - earthing of the midpoint of the DC source;
• 2 - open conductive parts;
• 3 - power supply

Rice. 1.7.2. TN-S system of alternating (a) and direct (b) current.

(click to enlarge)

Zero protective and zero working conductors are combined in one conductor in part of the system:

• 1 - grounding conductor of the neutral of the alternating current source;
• 1-1 - ground electrode of the output of the DC source;
• 1-2 - earthing of the midpoint of the DC source;
• 2 - open conductive parts;
• 3 - power supply

Rice. 1.7.3. TN-CS system of alternating (a) and direct (b) current.

(click to enlarge)

Exposed conductive parts of the electrical installation are earthed. The neutral of the power supply is isolated from earth or grounded through a high resistance:

• 1 - grounding resistance of the neutral of the power supply (if any);
• 2 - ground electrode;
• 3 - open conductive parts;
• 4 - grounding device of the electrical installation;
• 5 - power supply

Rice. 1.7.4. IT system of alternating (a) and direct (b) current.

(click to enlarge)

Exposed conductive parts of the electrical installation are grounded using grounding, electrically independent of the neutral grounding conductor:

• 1 - grounding conductor of the neutral of the alternating current source;
• 1-1 - ground electrode of the output of the DC source;
• 1-2 - earthing of the midpoint of the DC source;
• 2 - open conductive parts;
• 3 - ground electrode of open conductive parts of the electrical installation;
• 4 - power supply

Rice. 1.7.5. TT system of alternating (a) and direct (b) current.

1.7.4. An electrical network with an effectively grounded neutral is a three-phase electrical network with a voltage above 1 kV, in which the earth fault factor does not exceed 1,4.

The earth fault ratio in a three-phase electrical network is the ratio of the potential difference between an intact phase and earth at the earth fault point of another or two other phases to the potential difference between the phase and earth at that point before the fault.

1.7.5. Solidly grounded neutral - the neutral of a transformer or generator, connected directly to the grounding device. The output of a single-phase AC source or the pole of a DC source in two-wire networks, as well as the midpoint in three-wire DC networks, can also be dead-earthed.

1.7.6. Isolated neutral - the neutral of a transformer or generator that is not connected to a grounding device or connected to it through a high resistance of signaling, measuring, protection devices and other similar devices.

1.7.7. A conductive part is a part that can conduct an electric current.

1.7.8. Current-carrying part - the conductive part of the electrical installation, which is under operating voltage during its operation, including the zero working conductor (but not the PEN conductor).

1.7.9. Open conductive part - a conductive part of an electrical installation that is accessible to the touch and is not normally energized, but which may become energized if the main insulation is damaged.

1.7.10. Third-party conductive part - a conductive part that is not part of the electrical installation.

1.7.11. Direct contact - electrical contact of people or animals with current-carrying parts that are energized.

1.7.12. Indirect touch - electrical contact of people or animals with open conductive parts that are energized when the insulation is damaged.

1.7.13. Protection against direct contact - protection to prevent contact with live parts under voltage.

1.7.14. Indirect contact protection - protection against electric shock when touching open conductive parts that are energized when the insulation is damaged.

The term insulation failure should be understood as a single insulation failure.

1.7.15. Grounding conductor - a conductive part or a set of interconnected conductive parts that are in electrical contact with the ground directly or through an intermediate conductive medium.

1.7.16. Artificial ground electrode - a ground conductor specially made for grounding purposes.

1.7.17. Natural ground conductor - a third-party conductive part that is in electrical contact with the ground directly or through an intermediate conductive medium used for grounding purposes.

1.7.18. Grounding conductor - a conductor connecting the grounded part (point) with the ground electrode.

1.7.19. Grounding device - a combination of grounding and grounding conductors.

1.7.20. Zero potential zone (relative earth) - a part of the earth that is outside the zone of influence of any grounding conductor, the electric potential of which is assumed to be zero.

1.7.21. Spreading zone (local earth) - the earth zone between the ground electrode and the zone of zero potential.

The term earth used in the chapter should be understood as earth in the spreading zone.

1.7.22. An earth fault is an accidental electrical contact between energized live parts and earth.

1.7.23. The voltage on the grounding device is the voltage that occurs when current drains from the ground electrode into the ground between the point of current input into the ground electrode and the zone of zero potential.

1.7.24. Touch voltage - the voltage between two conductive parts or between a conductive part and the ground when a person or animal touches them at the same time.

Expected touch voltage - the voltage between conductive parts that are simultaneously accessible to touch when a person or animal does not touch them.

1.7.25. Step voltage - the voltage between two points on the surface of the earth, at a distance of 1 m from one another, which is taken equal to the length of a person's step.

1.7.26. The resistance of the grounding device is the ratio of the voltage on the grounding device to the current flowing from the grounding conductor into the ground.

1.7.27. Equivalent resistivity of the earth with a heterogeneous structure - the electrical resistivity of the earth with a homogeneous structure, in which the resistance of the grounding device has the same value as in the earth with a heterogeneous structure.

The term resistivity used in the chapter for non-homogeneous earth should be understood as equivalent resistivity.

1.7.28. Grounding - the intentional electrical connection of any point in the network, electrical installation or equipment with a grounding device.

1.7.29. Protective grounding - grounding performed for electrical safety purposes.

1.7.30. Working (functional) grounding - grounding of a point or points of current-carrying parts of an electrical installation, performed to ensure the operation of an electrical installation (not for electrical safety purposes).

1.7.31. Protective grounding in electrical installations with voltage up to 1 kV - a deliberate connection of open conductive parts with a dead-earthed neutral of a generator or transformer in three-phase current networks, with a dead-earthed output of a single-phase current source, with a grounded source point in DC networks, performed for electrical safety purposes.

1.7.32. Potential equalization - electrical connection of conductive parts to achieve equality of their potentials.

Protective equalization of potentials - equalization of potentials, performed for the purpose of electrical safety.

The term potential equalization used in the chapter should be understood as protective potential equalization.

1.7.33. Potential equalization - reducing the potential difference (step voltage) on the surface of the earth or floor with the help of protective conductors laid in the ground, in the floor or on their surface and connected to a grounding device, or by using special earth coatings.

1.7.34. Protective (PE) conductor - a conductor intended for electrical safety purposes.

Protective earth conductor - a protective conductor intended for protective earthing.

Potential equalization protective conductor - a protective conductor designed for protective potential equalization.

Zero protective conductor - a protective conductor in electrical installations up to 1 kV, designed to connect open conductive parts to a solidly grounded neutral of a power source.

1.7.35. Zero working (neutral) conductor (N) - a conductor in electrical installations up to 1 kV, designed to power electrical receivers and connected to the dead-earthed neutral of a generator or transformer in three-phase current networks, with a dead-earthed output of a single-phase current source, with a dead-earthed source point in DC networks.

1.7.36. Combined zero protective and zero working (PEN) conductors - conductors in electrical installations with voltage up to 1 kV, combining the functions of zero protective and zero working conductors.

1.7.37. The main ground bus is a bus that is part of the grounding device of an electrical installation up to 1 kV and is designed to connect several conductors for the purpose of grounding and potential equalization.

1.7.38. Protective automatic power off - automatic opening of the circuit of one or more phase conductors (and, if required, the zero working conductor), performed for electrical safety purposes.

The term auto power off as used in the chapter should be understood as protective auto power off.

1.7.39. Basic insulation - insulation of current-carrying parts, providing, among other things, protection against direct contact.

1.7.40. Additional insulation - independent insulation in electrical installations with voltage up to 1 kV, performed in addition to the main insulation for protection against indirect contact.

1.7.41. Double insulation - insulation in electrical installations with voltage up to 1 kV, consisting of basic and additional insulation.

1.7.42. Reinforced insulation - insulation in electrical installations with voltage up to 1 kV, providing a degree of protection against electric shock equivalent to double insulation.

1.7.43. Extra low (low) voltage (SLV) - voltage not exceeding 50 V AC and 120 V DC.

1.7.44. Isolating transformer - a transformer, the primary winding of which is separated from the secondary windings by means of protective electrical separation of circuits.

1.7.45. Safety isolating transformer is an isolating transformer designed to supply extra-low voltage circuits.

1.7.46. Protective screen - a conductive screen designed to separate an electrical circuit and / or conductors from the current-carrying parts of other circuits.

1.7.47. Protective electrical separation of circuits - separation of one electrical circuit from other circuits in electrical installations with voltage up to 1 kV using:

• double insulation;
• basic insulation and protective shield;
• reinforced insulation.

1.7.48. Non-conductive (insulating) premises, zones, sites - premises, zones, sites in which (on which) protection in case of indirect contact is provided by high resistance of the floor and walls and in which there are no grounded conductive parts.

See other articles Section Rules for the installation of electrical installations (PUE).

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